There is no shortage of lens adapters for smartphones, even of the macro variety, but generally they're too bulky and expensive to be worth the reward. Photojojo's solved both of those problems with a $15 rubber band that contains an embedded macro lens adapter.

To use it, you just strap the band around your smartphone and position the embedded adapter over your smartphone's camera lens. Once you do, you'll be able to take macro photos like you normally would. If you want to revert to your standard lens, just pull the band off. It's tiny so it's easy to store when you're not using it, and you can even wear it around your wrist. This is a great little upgrade if you love macro photography and don't want to commit to an accessory that only works on one type of device.